Osteoarthritis is a prevalent disease characterized mainly by cartilage degradation that is clinically reflected by a gradual development of joint pain, stiffness, and loss of motion. Osteoarthritis is extremely frequent in the general population, and it is estimated that its radiological prevalence is close to 50% overall. This figure is even higher in the elderly, with as much as 75% of the population between ages of 55 and 64 exhibiting some degree of radiological osteoarthritis in one or more joints. Although this disease is often benign, severe degenerative changes may cause serious disability.
Clinical osteoarthritis is now understood to be a complex interaction of degradation and repair of the cartilage, bone, and synovium, with secondary components of inflammation. The biochemical changes of osteoarthritis affect several cartilage components, including major matrix constituents, proteoglycans, and collagens. Decreased proteoglycan content in conjunction with damaged collagen structure leads to functional loss of normal matrix physiologic properties. Although the etiology of osteoarthritis is multiple and includes mechanical and biochemical factors, it appears that these culminate in an increased synthesis of proteolytic enzymes by the chondrocytes, which in turn leads to cartilage destruction.
There is no known cure for osteoarthritis, and current treatments are essentially limited to reliving the patient's symptoms. Research is under way, however, to find a therapeutic agent that will slow or stop the progression of the disease. One current approach to developing pharmacological treatments for osteoarthritis focuses on subchondral bone sclerosis, which is a well-recognized manifestation of osteoarthritis that could play a major role in the onset and/or progression of the disease.
Unfortunately, evaluating the efficacy of such agents is not an easy, straightforward process. For many years, studies of drug interventions on symptomatic knee osteoarthritis focused only on clinical parameters like pain and joint function, without assessing the anatomical impact of the disease (i.e., cartilage degradation and bone sclerosis). Simple radiographs are now often used in clinical trials for osteoarthritis to establish inclusion criteria, but such trials have not employed them to assess disease progression. More complex radiographic methods have also been proposed for measuring joint space width, such as the Buckland-Wight method, which may be used in clinical trials. Arthroscopy appears reliable and sensitive to changes, but it only allows for evaluation of the cartilage surface. It also appears to be somewhat subjective even when independently trained evaluators review video recordings of the procedures, and, above all, it is invasive.
A number of academic researchers have evaluated the use of Magnetic Resonance Imaging (MRI) for orthopedic investigations over the last ten years. Some researchers have proposed using MRI to reproducibly quantify articular dimensions to follow disease progression, and thereby assess whether proposed treatments may be responsible for changing the rate of cartilage loss. But the actual application of these proposed systems to the complex problem of making meaningful measurements on acutal diseased joints has not been shown to be entirely successful. This may be due to one or more of a variety of shortcomings, including extensive manual treatment and interpretation of data, excessive reliance on subjective human judgment, insufficient accuracy or repeatability to achieve meaningful results when used on actual diseased joints, inability to distinguish secondary symptoms, and/or excessively long scan times.